The conventional telecommunications network includes two distinct communication pathways or subnetworks—a voice network and a signaling network. These two networks function in a cooperative manner to facilitate communications between users. As implied by its name, the voice network handles the transmission of voice (or user data) information between users. The signaling network has a number of responsibilities, which include call setup, call teardown, and database access. In simple terms, the signaling network facilitates the dynamic linking together of a number of discrete voice-type communication circuits, such that a voice-type connection is established between the calling and called party. Additionally, the signaling network provides a framework through which non-voice-related information may be transported, with this data and transport functionality being transparent to the users. This signaling technique is often referred to as out-of-band signaling, where the term “band” implies voice band. The signaling protocol most commonly employed in communication networks around the world is the signaling system 7 (SS7) signaling protocol. Different variations of SS7 may be used in different regions.
From a hardware perspective, an SS7 network includes a plurality of SS7 nodes, generically referred to as signaling points (SPs), that are interconnected using signaling links, also referred to as SS7 links. At least three types of SPs are provided in an SS7 network: service switching points (SSPs), signal transfer points (STPs) and service control points (SCPs). Within an SS7 signaling network, such SP nodes are assigned an SS7 network address in the form of a point code (PC).
An SSP is normally installed in Class 4 tandem or Class 5 end offices. The SSP is capable of handling both in-band signaling and SS7 signaling. An SSP can be a customer switch, an end-office, an access tandem and/or a tandem. An STP transfers signaling messages from one signaling link to another. STPs are packet switches and are generally installed as mated pairs. Finally, an SCP provides access to databases, such as 800 number translation databases, 800 number carrier identification databases, credit card verification databases, etc.
Signaling links are transmission facilities used to connect one SP to another. Conventional signaling links are dedicated bidirectional facilities operating at 56 kbps in the U.S. and Canada and at 64 kbps when clear channel capability is deployed. The relatively recent emergence of Internet protocol (IP)-based telephony (i.e., IP telephony) has led to a number of new network elements, some of which communicate via both traditional public switched telephone network (PSTN) SS7 and IP based signaling protocols. For instance, a media gateway controller (MGC) is a network element that effectively serves as a bridge between the PSTN and an IP telephony network. That is, an MGC node communicates with and controls one or more media gateway (MG) nodes. Those familiar with PSTN network architectures will appreciate that the functionality provided by an MGC/MG pair (i.e., a “softswitch”) is similar to the functionality provided by a traditional PSTN tandem office switch. In the case of an MGC node, SS7 call control signaling messages (e.g., ISUP and TCAP messages) are received and processed by the MGC, which in turn uses one or more non-SS7 signaling protocols (e.g., MGCP, UNI 4.0, ALTA, etc.) to communicate with an associated MG node.
With particular regard to the SS7 protocol and the issue of SS7 protocol variants, it will be appreciated that in an international communications environment it is often the case that different countries employ variations of a common or standard call control protocol, such as the ISDN user part (ISUP) protocol. The different variations are referred to as ISUP variants. Such protocol variations pose significant problems for those network operators attempting to provide international connectivity.
In North America, ISUP messages and protocols are defined by Telcordia Technologies Specification of the Signaling System Number Seven, GR-246-CORE, Volume 3, T1.113.1-T1.113.5 (December 2001), the disclosure of which is incorporated herein by reference in its entirety. Likewise, in Europe, the International Telecommunications Union (ITU) Q.76x series of specifications defines the ISUP messages and protocols to be used by “international” signaling gateways. Within European non-gateway switching environments, the use of different ITU national ISUP variants is widespread. It will be appreciated that while this problem exists throughout the world, it is especially acute in Europe where practically each country employs its own ISUP variant.
In general, the differences from variant to variant may include differences in message types or sets of message types, differences in parameters or different sets of parameters being used in each message, and differences in the interpretation of the encoding of fields within message parameters. For example, there are approximately 45 message types and 62 parameters defined in the ITU Q.763 standard. Many of these parameters are used in multiple message types. Within all ISUP protocols there are essentially three types of message parameters: mandatory fixed (i.e., the parameter is of a fixed size and must be present in the message), mandatory variable (i.e., the parameter is of a variable size and must be present in the message), and optional. The combination of message type and the ISUP specification being used uniquely identifies the parameters that are applicable to a given ISUP message. That is, the message type and associated ISUP specification together imply the number and sequence of mandatory fixed and mandatory variable parameters. When a particular message contains more than one mandatory fixed parameter, the order of those parameters is fixed and is detailed in the relevant ISUP specification. Similarly, when a particular message contains more than one mandatory variable parameters, the order of those parameters is fixed and is detailed in the relevant ISUP specification. The order of optional parameters within an ISUP message is not fixed. Unlike the mandatory fixed and mandatory variable sections of the ISUP messages, the option parameter section provides the parameter ID as the first field within each parameter. Again, from variant to variant, different sets of messages are used, different sets of parameters are associated with a given message type, and different field and bit encoding schemes are associated with a given parameter.
ISUP protocol variants are not limited to country specific scenarios. For instance, different network operators within the same national network environment may implement or support slightly different variations of a common or standard call control protocol. This situation may occur in networks using IP telephony protocols.
FIG. 1 illustrates an exemplary international communication network architecture that employs both traditional SS7 and IP based signaling nodes. More particularly, FIG. 1 includes a British signaling network 100 and a German signaling network 101. British signaling network 100 includes a pair of end office signaling points 102 and 104, an SS7 signal transfer point (STP) 106, a gateway STP node 108, and a media gateway 112. Likewise, German signaling network 101 includes a pair of end office signaling points 122 and 124, an SS7 signal transfer point (STP) 126, a gateway STP node 128, and a media gateway 132. A media gateway controller node 130 facilitates international call setup and teardown.
In this example, it is assumed that a British ISUP protocol variant is employed in British signaling network 100, while a German ISUP protocol variant is employed in German network 101, and that these two ISUP protocol variants are different. As such, MGC node 130 must be capable of processing both British and German ISUP variant call signaling messages. In addition, extending this network architecture to include additional national networks requires that MGC node 130 be capable of processing an even greater number of ISUP variants. Such multiple protocol variant support is inherently complex, costly, difficult to administer, and is not particularly scalable with regard to the support of new or additional ISUP protocol variants (i.e., the support of new or additional national networks).
Therefore, what is needed is a system and method of minimizing the number of ISUP protocol variants that must be supported by a signaling message switching point (e.g., a media gateway controller or softswitch) that serves multiple communication networks employing different ISUP protocol variants.